Sinus infections may be acute or chronic and may develop because of a viral, bacterial, or fungal infection.

Lying behind your eyebrows, behind your cheekbones, and between your eyes are your sinuses — air-filled cavities lined with a mucous membrane that filters and humidifies the air you inhale.

This membrane produces and circulates mucus into your sinus and nasal passages to help remove dust, particles, and microbes from the air that you breathe. Tiny hair-like cells called cilia sweep the mucus to the openings that lead to the back of your throat, allowing it to slide down into your stomach. (1)

What Causes Sinus Infections or Sinusitis?

A sinus infection occurs when the sinuses (or, more specifically, the mucous membranes) become inflamed and swell up because of a viral, bacterial, or fungal infection. Sinus blockage often precedes this inflammation.

The terms "sinus infection" and "sinusitis" are commonly used interchangeably, but sinusitis simply refers to the inflammation of the sinuses, with or without an infection. The medical term for sinusitis is rhinosinusitis ("rhino" meaning "nose") because the illness affects the mucous membranes in both the sinuses and nose. (3,4)

How Common Are Sinus Problems and Chronic Sinus Issues?

Each year, acute (short-term) sinusitis affects about 31 million Americans, who spend a whopping $1 billion on over-the-counter medications and $150 million on prescription medications to cure the illness, according to the American College of Allergy, Asthma, & Immunology. (3)

Chronic (long-term) sinusitis is one of the most common chronic illnesses in the United States, affecting approximately 15 percent of the population, according to the American Rhinologic Society. (5)

How Long Does a Sinus Infection Last?

Sinusitis is usually classified as either acute or chronic.

Acute sinusitis causes inflammation and symptoms that often develop quickly and last 7 to 10 days if caused by a viral infection, but the illness can last for up to 4 weeks if it's caused by a bacterial infection.

Chronic sinusitis lasts for 12 weeks or more. This inflammation can continue for months or years more, and people often describe them as a never-ending cold. (1)

Sinusitis may also be classified as:

Subacute, in which symptoms last for more than 4 weeks but less than 12 weeks

Recurrent acute, in which there are at least four acute sinus infection episodes within one year

Acute exacerbation of chronic rhinosinusitis, in which symptoms worsen in a person with chronic sinusitis (5)

But having symptoms of sinusitis doesn’t always mean that you have a sinus infection.

Is It a Sinus Infection, Cold, or Allergy?

Colds, allergies, and sinus infections can cause similar symptoms, including stuffiness and headache. What's more, both colds and allergies can cause sinus inflammation. So how can you tell the difference between these illnesses?

The truth is, even doctors can sometimes have difficulty differentiating among colds, allergies, and sinus infections. But the illnesses do present differently.

A hallmark sign that you have a sinus infection is that the illness is, as you'd expect, severely affecting your sinuses. Both colds and allergies can cause congestion and runny nose, but sinus infections typically cause an aching sensation and pressure (feeling of fullness) in the face, including in the ears and teeth.

Additionally, postnasal drip (when mucus drips down the back of the throat), reduced sense of smell, and halitosis (bad breath) are typically associated with sinus infections.

The mucus associated with a sinus infection is usually green or yellow, though color alone isn't enough to determine the cause of your nasal distress, as there are many reasons your nasal discharge may not be clear. (6)

Both allergies and colds can cause sneezing, a symptom not typically seen in sinus infections. Allergies never cause fever, which is seen in both colds and sinus infections.

And if your symptoms last more than 10 days, you most likely don't have a cold. (7)

Are Sinus Infections Contagious?

A sinus infection is not exactly contagious. But depending on what caused a person's inflammation, other people may also develop the illness.

Sinus infections ultimately develop because of sinus and nasal blockages.

In healthy people, mucosal secretions are always moving and draining into the nasal cavity. But when blockage occurs, mucus fails to drain properly, increases in thickness, and fills the sinus spaces.

The cilia also slow down their sweeping and cleaning, making it even harder for mucus to drain.

When the mucus is unable to drain, it becomes the perfect medium for microbes to grow out of control and cause an infection.

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Some Root Causes of Sinus Blockage

There are several underlying causes of sinus blockage, including various environmental, anatomical, and genetic factors. But the most common cause of the blockage is inflammation or swelling of the nasal passages because of the common cold or allergies. (9)

This virus may jump to other people, causing a cold that may also develop into viral sinusitis. (11)

In only 0.5 to 2 percent of cases do people develop bacterial sinusitis (a sinus infection caused by bacteria), which is typically a complication of viral sinusitis. Bacterial sinusitis is not contagious. (10)

In rare cases, fungi can cause a sinus infection, particularly if a person has a fungal allergy. But fungal sinusitis is not often seen in people with healthy immune systems. (12)

Top Causes of Sinus Inflammation, Swelling, and Stuffiness

There are numerous causes of sinus blockage and inflammation, which can make sinus infections more likely.

Types of Chronic Sinusitis or Chronic Sinus Infections

While acute sinusitis often involves an infection, chronic sinusitis does not. Sometimes, the long-term illness is caused by an infection that hasn't cleared up properly, but most often the exact cause of chronic sinusitis isn't known. (4)

But clinicians may categorize chronic sinusitis into one of three types depending on the features present.

The most common type of the illness, chronic sinusitis without nasal polyposis, involves swelling and inflammation of the mucous membranes by various nonpolyp factors, such as allergies or irritation (from airborne allergens and toxins) and infections.

Chronic sinusitis with nasal polyposis, on the other hand, involves nasal polyps that are large enough to clog the sinus. It's not always clear why some people develop these polyps and others don’t.

In chronic sinusitis with fungal allergy, people experience a strong allergic reaction to fungi in the air, which causes their mucous membranes to produce a thick, dense mucus.

Risk Factors for Chronic Sinusitis and Recurring Sinus Infections

Whatever the type, several factors can increase a person's risk of developing chronic sinusitis or make the symptoms worse, including:

On the other hand, a secondary acute bacterial infection may develop, so it's advised that you see a doctor if your symptoms last more than 10 days or if your symptoms initially improve but then worsen again within the first 7 days.

Learn what causes otherwise imperceptible substances to become a noticeable bother.

Try to Ease Your Sinus Symptoms and Heal at Home

Especially if you deal with recurring sinus problems, you’ll want to experiment to find out which are the best home remedies and therapies for you. If you are dealing with nasal congestion and aches, check out these natural approaches to relieve sinus pain and pressure.

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